The growing popularity of parallel processing and the development of large networks of intercommunicating electrical and electromechanical devices have led to the search for a switching system that is capable of handling interconnections for a high density of data transfer between subscribers and that is able to ensure connection of all non-competing requests with minimum delay. The present invention provides a switching system which meets these demands. The background of this invention relates to the fields of optics and communication switching systems.
The field of optics has progressed considerably since the invention of lens systems that were designed for magnification and projection of light images. Optics today encompasses a wide range of equipment and operations, including a variety of lens and prism systems, analog optical processors, fiber optics and optical waveguides, and digital or numerical optical computers.
Imaging is vital to the operation of most modern optical systems. Of particular interest are relay-field lens systems, because these systems allow propagation of an image over a long path without divergence of the light beam, therefore conserving light.
The spatial Fourier transform capabilities of a lens is well known today. The development of optical detectors and light emitting diodes has led to widespread use of optical systems in Fourier transform configurations for analog computing with light. This procedure is especially useful in spectrum analysis and pattern recognition.
A great deal of research has been applied to the field of fiber optics and optical waveguides. Optical fibers allow fast communication with low attenuation over long distances, and optical waveguides are now being used in integrated optical systems to achieve switching between two optical communication lines by coupling techniques. Both of these devices allow a larger bandwidth for communication, in part, because of the optical carrier frequencies that are used.
Perhaps the newest and most exciting developments in optics have been in the area of digital optical computing. The development of real time image transducers, usually called spatial light modulators, has led to a major advancement in optical processing. In much the same manner as electronic processing, optical computing has progressed from analog systems to digital or numerical systems. Digital optical computers show promise of being much more versatile than analog systems, for the same reasons that digital electronic computers are more versatile than their analog predecessors. In addition, the spatial light modulators allow processing with arrays of independent image elements at one time through parallel processing.
Components of digital optical computers are developed as a result of use of spatial light modulators, which allow the intensity of light images projected onto one area of them to control light images projected through them or reflected off them, much in the same way transistors or diodes control output voltages as a function of input voltages. This characteristic of the spatial light modulator has enabled the fabrication of optical logic gates, flip-flops, and operational amplifiers. The advantage to such optical devices is the parallel nature of the two-dimensional input and output to them. Complete arrays of image elements are processed through arrays of logic gates at the same time, using the same lenses, polarizers, mirrors, and spatial light modulator.
Contemporary switching systems for connection of communication lines between intercommunicating electronic or electromechanical devices such as minicomputers or telephones interconnected in a network are generally one of two types. These systems are commonly known as store and forward systems or circuit switching systems. A third switching system, using optical waveguide principles, is known to be under development.
Store and forward systems involve moving data bursts through a switching lattice one node at a time while storing the message at each node along the path until a route to the next node is clear. These systems do not require a constant path from message source to message receiver, but allow the message burst to follow the first available path from node to node until the destination is reached.
Circuit switching systems provide a continuous path for two-way communication between two subscribers. Common types of circuit switching systems include electro-mechanical step-by-step and crossbar switching, and electronic switching.
Optical waveguide switching systems are in development stages and provide switching between two or more optical paths by controlled coupling techniques. These systems differ from the optical switching system of the present invention because the optical waveguide systems cannot operate on image arrays, but channel information along separate serially coded paths.
The present invention relates to a parallel processing optical switching system for intercommunicating electronic or electromechanical devices. This system does parallel processing by virtue of the imaging optics, which are used both for control and connection operations. The system operates with the incorporation of digital optical computing, and uses a spatial light modulator as a control device. The system uses all aspects of optics including imaging, Fourier transforming, and optical logic gates and flip-flops. The logic design has an obvious electronic analog. The switching network is of the circuit switching type.
The design requirements for the optical switching system of the present invention are a result of the characteristics of the network of intercommunicating electronic or electromechanical devices in which the system is intended to be used. These network characteristics include the network size and form of control information supplied to the switching system, user protocol that is assumed by the system, a model of the network, and a description of the type of communication transfer between subscribing devices.
The switching system of the present invention, assumes that the network comprises a star configuration with a plurality of subscribers. Addressing information for a connection request is not coded for the switching system, described herein, therefore a separate line for each possible destination address is supplied for each subscriber for initiating a request.
The switching operation of the present invention is designed for use of the following user protocol. A connection request is originated by activating the address lead of the desired destination subscriber. After a set time interval, the originating subscriber samples a status lead to determine if the request has been approved by the switching system. If the system has approved the request, the originating subscriber waits for a handshaking message on its data reception line from the destination subscriber. After communication is complete, the originating subscriber signals the switching system to disconnect by removing its connection request. The destination subscriber simply responds to a request interrupt supplied by the switching system by answering the origination subscriber with a handshake signal on its data transmission line.
The network of subscribers for which the optical switching system is designed is characterized as a star or hub with the electrical or electromechanical subscribers being modelled as satellites connected to a central unit. The subscribers are located in a circle around the switching system, and communication between different N subscribers is accomplished by establishing a line to the switching system from the subscriber requesting a connection and a line from the switching system to the subscriber that is being requested for communication. In this operation, the subscriber originating the call (originator) supplies the switching system with addressing information to connect a path to the requested subscriber (destination). The switching system responds by checking to see if the destination is not connected, and if so by allotting a path from the originator to the switching system and a path from the switching system to the destination.
The type of communication between subscribers in the network is characterized by the directions of message transfer and the type of messages being transferred. Two-way communication between subscribers involved in a connection is assumed for the network of the present invention. The switching system automatically allots a path for return communication from the call destination subscriber through the switching system to the call originating subscriber. The messages sent between the subscribers can range in length from short burst to long messages such as file transfer.
Switching systems are classified with respect to a number of different parameters. For instance, store and forward switching systems are inconvenient for both long messages and two-way communication transfer. Therefore, the circuit switching system is chosen for the optical application, that is providing constant communication paths between communicating subscriber pairs. In addition, the optical switching system is non-blocking in that every request for connection with an idle destination subscriber is completed. The system is not progressive in nature, because system control is parallel and the addressing of the destination for the request is immediately available to the system. The present invention is considered a direct control system, because a requested address for a destination subscriber designates the specific path that the data transfer takes through the switching system.
Although conventional circuit switching systems can be fast enough to handle certain communication connections, they are only capable of completing one connection at a time. In situations such as those with heavy traffic through the switching system, the call connections are either blocked by the system and refused or queued in some manner until the system can process the call. For telephony this is not normally a problem, because the switching speed is still fast enough to avoid any perceivable delay. For connections between computers in a network, however, delay time for heavy traffic periods is appreciable. For this reason, the optical switching system of the present invention has been developed. The parallel processing capabilities of the optical switching system will connect an arbitrary number of call requests and handle those call requests asyncronously and completely independently with respect to each other.
The optical switching system of the present invention is based on a crosspoint matrix. Although the system is based on a crosspoint matrix, the physical means of connection for the communication lines is quite different from the approach used in crossbar systems. The optical switching system employs matrix-vector multiplication techniques to connect the lines simultaneously and at the speed of light. In addition, the imaging optics allow the control circuitry to be parallel processing, providing more efficient use of control equipment.
The present invention comprises a switching system that is capable of processing communication connections between an arbitrary number of electronic or electromechanical subscribers in a network of N subscribers simultaneously and completely independently. The advantage of such a parallel processing switching system is the elimination of queing delay presented by serially operating switching systems. The added feature that the switching system is optical allows the communication between subscribers to be accomplished at much higher data rates.